1. Field of the Invention
The present invention relates to a multidirectional time-division multiplexing wireless data communications system, and more specifically to a multidirectional time-division multiplexing wireless data communications system for fixedly assigning a wireless time slot used between a first station and a second station, for example, between a parent station and a child station, and establishing communications between plural pieces of data terminal equipment connected to the stations.
2. Description of the Related Art
In a wireless system for establishing multidirectional time-division multiplexing communications, the one-to-N time-division multiplexing communications are established between a parent station and a plurality of child stations which communicate with the parent station.
At this time, in the telephone communications using a system in which both telephone communications and data communications are set, a channel assigning process is controlled by a demand-assign system for assigning a wireless communications channel between the parent station and the child stations only when a call is issued from the parent station or the child stations.
In the data communications, the channel assigning process is controlled by the pressing system for preliminarily and fixedly assigning a wireless communications channel for use in the data communications between data terminal equipment connected to the parent station and data terminal equipment, connected to a child station, for communicating with the data terminal equipment connected to the parent station.
FIG. 5 is a block diagram of the configuration of the conventional multidirectional time-division multiplexing wireless data communications system. The multidirectional time-division multiplexing wireless data communications system shown in FIG. 5 includes a parent station 1, plural pieces of data terminal equipment 1a, 1b, and 1c connected to the parent station 1, child stations 10, 11, and 12 for performing wireless communications with the parent station 1, and data terminal equipment 10a, 11a, and 12a connected to the child stations 10, 11, and 12.
The data communications are performed by a time-division multiplexing system (hereinafter referred to as a TDM system) in the;downstream from the parent station 1 to the child stations 10 through 12 while the data communications are performed by a time-division multiple attachment system (hereinafter referred to as a TDMA system) in the upstream from the child stations 10 through 12 to the parent station 1.
Described below are the operations in which the data terminal equipment 1a and the data terminal equipment 10a; the data terminal equipment 1b and the data terminal equipment 11a; and the data terminal equipment 1c and the data terminal equipment 12a communicate with each other respectively.
First, a wireless time slot for use as a wireless communications channel is preliminarily and fixedly assigned to each data terminal equipment.
That is, a wireless time slot TS0 is fixedly assigned to the data terminal equipment 1a and the data terminal equipment 10a, a wireless time slot TS1 is fixedly assigned to the data terminal equipment 1b and the data terminal equipment 11a, and a wireless time slot TS2 is fixedly assigned to the data terminal equipment 1c and the data terminal equipment 12a. 
As shown in FIG. 6, the wireless time slot TS0, the wireless time slot TS1, and the wireless time slot TS2 are assigned to separate positions without overlapping each other about a time axis, and the signals transmitted through respective time slots do not crash each other.
When a call is issued to any data terminal equipment in the multidirectional time-division multiplexing wireless data communications system, the data communications can be established between corresponding data terminal equipment because a wireless time slot is assigned to each data terminal.
In the downstream data transmission, data signals transmitted from the data terminal equipment 1a, the data terminal equipment 1b, and the data terminal equipment 1c are input to the parent station 1, multiplexed by the parent station 1, and then transmitted to the child station 10, the child station 11, and the child station 12 by the TDM system.
That is, a data signal from the data terminal equipment 1a is multiplexed to the wireless time slot TS0, a data signal from the data terminal equipment 1b is multiplexed to the wireless time slot TS1, and a data signal from the data terminal equipment 1c is multiplexed to the wireless time slot TS2. Thus, the multiplexed burst data signals are transmitted to the child stations 10 through 12 by the TDM system.
The same signals are transmitted to the child stations 10 through 12.
Each of the child stations 10 through 12 retrieves, by separating and selecting, the data signal addressed to itself, and transmits the data signal to the connected data terminal equipment.
That is, the data signal multiplexed to the wireless time slot TS0 is separated by the child station 10 and transmitted to the data terminal equipment 10a, the data signal multiplexed to the wireless time slot TS1 is separated by the child station 11 and transmitted to the data terminal equipment 11a, and the data signal multiplexed to the wireless time slot TS2 is separated by the child station 12 and transmitted to the data terminal equipment 12a. 
In the upstream data transmission, a data signal from the data terminal equipment connected to the child station is multiplexed to a wireless time slot assigned by each child station, and transmitted to the parent station as a burst signal by the TDMA system.
That is, the data signal from the data terminal equipment 10a is ;input to the child station 10, multiplexed to the wireless time slot TS0, and transmitted to the parent station 1.
Similarly, the data signal from the data terminal equipment 11a is input to the child station 11, multiplexed to the wireless time slot TS1, and transmitted to the parent station 1. The data signal from the data terminal equipment 12a is input to the child station 12, multiplexed to the wireless time slot TS2, and transmitted to the parent station 1.
The parent station 1 separates and retrieves the data signal from each of the child stations 10 through 12, and transmits the corresponding data signal to the connected data terminal equipment.
That is, the data signal multiplexed to the wireless time slot TS0 is transmitted to the data terminal equipment 1a, the data signal multiplexed to the wireless time slot TS1 is transmitted to the data terminal equipment 1b, and the data signal multiplexed to the wireless time slot TS2 is transmitted to the data terminal equipment 1c. 
For convenience in explanation in reference to FIG. 5, the number of child stations is set to 3, and the number of pieces of data terminal equipment connected to each of the child stations 10 through 12 is set to 1. The circuit, signal line, etc. that are not specifically important are omitted here. However, the similar operations are performed on the case in which the number of child stations is other than 3, and in which plural pieces of data terminal equipment are connected to one child station.
Described below is a one-to-one data transmitting operation. FIG. 7 shows the most popular conventional technology of this type.
In the first station, according to a timing signal generated by a timing signal generation circuit (TIM GEN) 22, a low-speed continuous signal SIG1 input from the data terminal equipment is input to a continuous/burst signal conversion circuit (C/B CONV) 21 in which the data is stored.
The timing signal generation circuit 22 generates a timing signal required when the low-speed continuous signal SIG1 is periodically input to the continuous/burst signal conversion circuit 21.
The data stored in the continuous/burst signal conversion circuit 21 is read according to the timing signal generated by a timing signal generation circuit 24, and transmitted to a wireless area as a high-speed burst signal SIG2.
The timing signal generation circuit 24 generates a timing signal required when the data stored in the continuous/burst signal conversion circuit 21 is periodically read in units of bits required by the unit burst data from the clock signal synchronous with the high-speed burst signal SIG2 on the wireless side.
That is, the timing between the low-speed continuous signal SIG1 and the high-speed burst signal SIG2 is shown in FIGS. 8A, 8B, 8C, and 8D.
In the second station, when the high-speed burst signal SIG2 (shown in FIG. 8A) transmitted from the continuous/burst signal conversion circuit 21 for converting the low-speed continuous signal SIG1 as shown in FIG. 8A into a high-speed burst signal is transmitted from the first station, it is received as a burst signal SIG3 (FIG. 8C) through a wireless area, and input to a burst/continuous signal conversion circuit 31 according to a timing signal generated by a timing signal generation circuit 32 in which a burst signal is stored.
The timing signal generation circuit 32 generates a timing signal required when the burst signal SIG3 is periodically input in units of bits required by the unit burst data from the clock signal synchronous with the burst signal SIG3 to the burst/continuous signal conversion circuit 31.
The data stored in the burst/continuous signal conversion circuit 31 is read by the timing signal generation circuit 35 according to a generated timing signal, and is output to the data terminal equipment as a low-speed continuous signal SIG4.
A timing signal generation circuit 35 generates a timing signal required when the data stored in the burst/continuous signal conversion circuit 31 is periodically read from the clock signal synchronous with the low-speed continuous signal SIG4.
That is, the timing between the burst signal SIG3 and the low speed continuous signal SIG4 is shown in FIGS. 8C and 8D.
As described above, regardless of the direction from the parent station to the child station, or from the child station to the parent station, similar operations can be performed in either direction.
In the conventional multidirectional time-division multiplexing wireless data communications system as shown in FIG. 7, the velocity of only the low-speed continuous data on the data terminal equipment side and the high-speed burst data on the wireless area side is converted, and the data is transmitted through the wireless area. Therefore, when interference or phasing occurs, its influence directly reaches the system, thereby generating a data signal bit error.
As a result, there arises the problem that an erroneous data signal is transmitted through a data communications line.
The present invention has been developed to solve the above described problems with the conventional technology, and aims at providing a multidirectional time-division multiplexing wireless data communications system capable of attenuating the influence of a bit error even if it occurs in a data signal to be transmitted due to the interference or phasing generated in the wireless area.
To attain the above described purpose, when the first station receives a low-speed continuous signal at the continuous/burst signal conversion circuit from the data terminal equipment in the multidirectional time-division multiplexing wireless data communications system according to the present invention, the signal is stored in the circuit, and converted into a high-speed burst signal. At the same time, the error correcting code circuit performs an error correcting code operation on a continuous signal in units of bits required by the unit burst data, and outputs an error correcting redundant bit.
The burst signal read from the continuous/burst signal conversion circuit is multiplexed to a predetermined wireless time slot preliminarily assigned by the multiplexing circuit. Simultaneously, the error correcting redundant bit output from the error correcting code circuit is multiplexed to a specific vacant slot in a wireless frame, and is transmitted as a high-speed burst signal to a wireless area.
On the other hand, in the second station, the burst/continuous signal conversion circuit temporarily stores a high-speed burst signal transmitted from a multiplexing circuit through a wireless area, and reads it as a low-speed continuous signal.
The read low-speed continuous signal is input to a division circuit. The division circuit divides a bit string forming an error correcting code in a continuous signal by a predetermined polynomial, and generates a syndrome for the error correcting code.
Based on the syndrome, an error position detecting circuit specifies a position at which a bit error has occurred in the data, and outputs it to the addition circuit.
According to the low-speed continuous signal read from the burst/continuous signal conversion circuit, the addition circuit inverts the bits detected by the error position detecting circuit at the position where the error has occurred, thus correcting the error.